Day: December 25, 2014

It might be good if I can get audio signals from IC-7410 in my rig control program. I used to use APIs provided by JACK, but this time I am trying with ALSA.

This could be a starting point for a beginner, so let’s see an example, pcm.c.

/*
 *   Transfer method - asynchronous notification
 */
struct async_private_data {
        signed short *samples;
        snd_pcm_channel_area_t *areas;
        double phase;
};
static void async_callback(snd_async_handler_t *ahandler)
{
        snd_pcm_t *handle = snd_async_handler_get_pcm(ahandler);
        struct async_private_data *data = snd_async_handler_get_callback_private(ahandler);
        signed short *samples = data->samples;
        snd_pcm_channel_area_t *areas = data->areas;
        snd_pcm_sframes_t avail;
        int err;
        
        avail = snd_pcm_avail_update(handle);
        while (avail >= period_size) {
                generate_sine(areas, 0, period_size, &data->phase);
                err = snd_pcm_writei(handle, samples, period_size);
                if (err < 0) {
                        printf("Write error: %s\n", snd_strerror(err));
                        exit(EXIT_FAILURE);
                }
                if (err != period_size) {
                        printf("Write error: written %i expected %li\n", err, period_size);
                        exit(EXIT_FAILURE);
                }
                avail = snd_pcm_avail_update(handle);
        }
}
static int async_loop(snd_pcm_t *handle,
                      signed short *samples,
                      snd_pcm_channel_area_t *areas)
{
        struct async_private_data data;
        snd_async_handler_t *ahandler;
        int err, count;
        data.samples = samples;
        data.areas = areas;
        data.phase = 0;
        err = snd_async_add_pcm_handler(&ahandler, handle, async_callback, &data);
        if (err < 0) {
                printf("Unable to register async handler\n");
                exit(EXIT_FAILURE);
        }
        for (count = 0; count < 2; count++) {
                generate_sine(areas, 0, period_size, &data.phase);
                err = snd_pcm_writei(handle, samples, period_size);
                if (err < 0) {
                        printf("Initial write error: %s\n", snd_strerror(err));
                        exit(EXIT_FAILURE);
                }
                if (err != period_size) {
                        printf("Initial write error: written %i expected %li\n", err, period_size);
                        exit(EXIT_FAILURE);
                }
        }
        if (snd_pcm_state(handle) == SND_PCM_STATE_PREPARED) {
                err = snd_pcm_start(handle);
                if (err < 0) {
                        printf("Start error: %s\n", snd_strerror(err));
                        exit(EXIT_FAILURE);
                }
        }
        /* because all other work is done in the signal handler,
           suspend the process */
        while (1) {
                sleep(1);
        }
}

Looks reasonable, isn’t it? So shall we begin?